Why is Fluent NHibernate ignoring my convention?

Question

I have a convention UserTypeConvention<MyUserType> where MyUserType : IUserType where MyUserType handles an enum type MyEnum. I have configured Fluent NHibernate thusly

sessionFactory = Fluently
                .Configure()
                .Database(MsSqlConfiguration.MsSql2005.ConnectionString(
                    c => c.Is(connectionString))
                )
                .Mappings(
                    m => m
                            .FluentMappings
                                .AddFromAssemblyOf<A>()
                            .Conventions
                                .AddFromAssemblyOf<A>()
                )
                .BuildSessionFactory();

where A is a type in the same assembly as UserTypeConvention<MyUserType> and MyUserType. However, Fluent NHibernate is not applying MyUserType to properties of type MyEnum on my domain objects. Instead, it is applying FluentNHibernate.Mapping.GenericEnumMapper<MyEnumType> to these properties.

What is going on?

Answer 1

For now I have solved this with:

public class MyEnumUserTypeConvention : UserTypeConvention<MyEnumUserType> {
    public override void Accept(IAcceptanceCriteria<IPropertyInspector> criteria) {
        // Fluent NHibernate is too eager in applying GenericEnumMapper
        // so our criteria is that it is already applied this type
        criteria.Expect(x => x.Type == typeof(GenericEnumMapper<MyEnum>));
    }

    public override void Apply(IPropertyInstance instance) {
        // we override Fluent NHibernate's application of GenericEnumMapper
        instance.CustomType<MyEnumUserType>();
    }
}

I think this should be thoroughly unnecessary. If someone told me this were a bug in Fluent NHibernate, that'd be fine. If someone gave me a good reason why Fluent NHibernate should be so eager in applying GenericEnumMapper that would be acceptable too.